The Place to Start for Operating System Developers
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int IamInt;
int IamLow;
int IamHigh;
IamInt = 0xAAAA5555;
IamLow = IamInt & (0x0000FFFF);
IamHigh = IamInt & (0xFFFF0000);
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#define HIBYTE(Value) Value >> ((sizeof(Value) << 0x03) - (sizeof(char) << 0x03))Integer is a type that depends of the OS (or mode).XCHG wrote:On x86 IA-32, Integer is normally known as a 32-bit (signed) value. This table might help you better:
Nibble = 4 Bits
Byte = 2 Nibbles = 8 Bits.
Word = 2 Bytes = 4 nibbles = 16 Bits.
Integer (also known as DWORD on IA-32) = 2 Words = 4 Bytes = 8 Nibbles = 32 bits.
Quad Word (also known as INT64 or QWORD) = 2 DWORDs = 4 Words = 8 Bytes = 16 Nibbles = 64 bits.
Does that help?
Allow me to rephrase thatMasterkiller wrote: Integer is a type that depends of the OS (or mode).
Integer and other data-types depend on the compiler and the architecture rather than the OS. The OS, I believe, must adhere to the architecture's convention of names for data-types. For example, in IA-32 Intel manuals, a Double Word or a DWORD is always 32-bits. An Operating System will only cause confusion to its users if it knows DWORD as a 64-bit or for example a 16-bit integral value. 
Ok, to shoot at the obvious lets assume i pass 0xDEADFEED at this macro.XCHG wrote:This one could run independent of the size of the value that it is passed to:
So you could pass 1-byte, 2-bytes, 4-bytes, 8-bytes ... values to it and it will still be able to find the high byte. It could have been written better but I didn't have time.Code: Select all
#define HIBYTE(Value) Value >> ((sizeof(Value) << 0x03) - (sizeof(char) << 0x03))
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int test = 0xDEADFEED;
if(HIBYTE(test) != 0xDE) {
printf("this macro is faulty\n");
}JamesM wrote:You should find that most OSs that follow POSIX like naming conventions almost* never use "int", "long". They use typedefs like "ptr_t", "pid_t" etc, and expect you to retrieve their values from the provided header files.
The answer is to use uint32_t et al., then you will never be confused!
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#include <iostream>
const int BitsPerByte = 8; // change this for your architecture
int main()
{
std::cout << "A char is a " << sizeof(char) * BitsPerByte << " bit value.";
std::cout << "A short int is a " << sizeof(short int) * BitsPerByte << " bit value.";
std::cout << "A long int is a " << sizeof(long int)* BitsPerByte << " bit value.";
std::cout << "A long long int is a " << sizeof(long long int) * BitsPerByte << " bit value.";
std::cout << "This computer uses " << sizeof(void *) * BitsPerByte << " bit addressing.";
return 0;
}
What exactly was that meant to signify?MessiahAndrw wrote:JamesM wrote:You should find that most OSs that follow POSIX like naming conventions almost* never use "int", "long". They use typedefs like "ptr_t", "pid_t" etc, and expect you to retrieve their values from the provided header files.
The answer is to use uint32_t et al., then you will never be confused!Code: Select all
#include <iostream> const int BitsPerByte = 8; // change this for your architecture int main() { std::cout << "A char is a " << sizeof(char) * BitsPerByte << " bit value."; std::cout << "A short int is a " << sizeof(short int) * BitsPerByte << " bit value."; std::cout << "A long int is a " << sizeof(long int)* BitsPerByte << " bit value."; std::cout << "A long long int is a " << sizeof(long long int) * BitsPerByte << " bit value."; std::cout << "This computer uses " << sizeof(void *) * BitsPerByte << " bit addressing."; return 0; }